This maybe what your looking for Kind of pricey at $135.00 from Automationdirect.comhttp://www.automationdirect.com/stat...rox30mmuhz.pdf
A ultrasonic proximity sensor can measure fluid levels from the top down, would make a great little addition to an HMI screen to show liquid level in the HLT.
Let me know if you go that route how it works out for you I have played with them a little here and there but never actually used it in a application.

I don't get how you could measure fluid levels using that, without using a whole bunch of them lined up in series. Does it return a gradient voltage or current based on the proximity?

This maybe what your looking for Kind of pricey at $135.00 from Automationdirect.comhttp://www.automationdirect.com/stat...rox30mmuhz.pdf
A ultrasonic proximity sensor can measure fluid levels from the top down, would make a great little addition to an HMI screen to show liquid level in the HLT.
Let me know if you go that route how it works out for you I have played with them a little here and there but never actually used it in a application.

I've helped used something similar in a CAT plant to position an end mill on an engine block. It wasn't for liquids, but it was pretty neat. Extremely accurate. Quite a bit of overkill for this scenario.
*EDIT* I did not look at the link and assumed it was something else. The one we used was a single sensor that bounced a signal back to determine distance.

Do you fly sparge? You don't lose heat during that? I haven't got my system up yet, but fully intend to run the HLT element while sparging to keep the temp of the sparge water where I want it. On my old propane system I only had a single burner, so while I was sparging I would move the burner to my boil kettle and get the boil started. By the time I was done sparging, the sparge water was probably 110-120 degrees at best.

I batch sparge.

When I'm ready to sparge, I add half the water and recirculate for a while. Then, after it drains, I add the other half. If I need to bump up the heat, I just turn the elements (heatsticks) back on in between halves.

I'm going to add a layer of reflectix insulation to the HLT, which will help with any heat loss.

You would only need 1 per vessel as it is analog, you would mount in the lid of your HLT, and you would need a analog input in order to read the sensor. In other words its not acutally a switch it is a analog measuring device like a thermocouple or pressure feedback, and could still function as a switch when certain levels were reached, but could also function as a level indicator when coupled with an HMI or similar device.

You would only need 1 per vessel as it is analog, you would mount in the lid of your HLT, and you would need a analog input in order to read the sensor. In other words its not acutally a switch it is a analog measuring device like a thermocouple or pressure feedback, and could still function as a switch when certain levels were reached, but could also function as a level indicator when coupled with an HMI or similar device.

If you dont want to put anymore hols in your kettle, why not just mount a float switch to a piece of tubing (stainles or acrylic if your cheap). Then just mount it to a cross that covers the opening. With that you could be in it for pretty cheap.. (less than 15 bucks if you use PVC cross, acrylic tube, and cheapo float switch. )